Motor speed-regulator.



A. A. TIRRILL.

MOTOR SPEED REGULATOR.

I APPLICATION FILED JAN. 9, 1909.

1 029,480. Patented June 11, 1912.

2 SHEETS-SHEET l.

Witnesses: ln'vzniior -64u/ Allen A.Tir| ill,

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A. A. TIRRILL. MOTOR SPEED REGULATOR. APPLICATION FILED JAILB, 1909.

1,029A80', Patented June 11, 1912.

2 SHEETS-SHEET 2.

Fig. 5.

Fig. 4

FREQUENCY igj isnessa: mvenmr Allen ATim'H,

UNITED s-TATEs Parana? orrron;

OF SCHER EC'TADY, NEW YORK, ASSIGNOR T GENERAL ELECTRIC COMPANY, A. CORPORATION OF NEW YORK.

moron SPEED-REGULATOR.

. To all whom it may concern: 7

Be it known that I, ALLEN A. TIRRILL a citizen of the United States, residing at Schenectady, county of Schenectady, State of New. York, have invented certain new and useful improvements in Motor Speed- Regulators, of which the following is a specification.

is desirable in some instances to maintain the speed ot a motor constant under conditions of'varying load or varying impressed voltage. the is well lmown, the

counter-electromotive force generated in the armature coils of a motor varies with the speed at which the rndtor is running and with the strength of the field. llhe energy consumed by the motor. is proportionate to the diderence between the impressed electromotive. force and the counter-electrometive force. Therefore, if either the load or the impressed voltage on the motor varies the speed varies until the counter-electromot-ive force has changed to the new value ening it with an increase of load, so that the .counter-electromotive force may fall without a decrease of speed.

According to my invention the speed of the motor is maintained constant by inserting and removing resistance in its field circult by means'of an electrically operated switch, which is vactuated by current derived from an alternating-current generator, driven by themotor. The inductance and capacity .in the circuit of the electrically operatedswitch areso proportioned that the circuit resonant to a frequency higher than the normal, frequency of the alternating current generated by the alternator when the motor isrunning at normal speed.

Therefore, as the speed of the motor tends to vary and the frequency'of the alternating current tends to increase, so asto approach,

or tends to decrease, so as to. recede from the frequency of resonance, the current in' the switch-controlling circuit will vary accordingly, increasing as the frequency ap- Specification of Letters Patent.

Application filed January 9, I909. Serial No.

.0 rating on the Patented June 11, 1912. 471,381.

proaches nearer to'the frequency at which the circuit is resonant, and decreasing as it recedes from the frequency for which the circuit'is resonant. ternating current likewise varies with the change of speed of the motor driving the alternating-current generator, the voltage rising with tne increase of speed and falling with a decrease of speed. The power of the magnet controlling the switch is thus afiected by two varying factors, the frequency and the voltage of the alternatingcurrent generator, both varying directly with the speed of the motor, andit is by this means made very sensitive to changes in speed. The alternating-current generator may be a small machine, which is either mounted on the same shaft as the motor, or connected to the same b belting, or in some other suitable way. it 1t is desired to make the regulation still more sensitive the speed of the alternating-current generator may he made greater than that of the motor driving the same, by suitable gearing. in some cases it is not necessary to provide a separate The voltage of the algenerator, as when the speed of a motorgenerator set, consisting of a direct-current motor and alternating-current generator, is

to be maintained constant, since in this case the switch, of course, can be operated by current derived from the a1lternating-current machine.

In the attached drawings, Figure l is a diagram of circuits, illustrating my invention in its simplest form; Fig. 2' is a fragmentary view, showing the alternating-current generator geared up to rotate at a higher speed than the motor; Fig. 3 shows a modified system in which the motor is provided with a se arate excite-r, the switch 0 inc; and Fig. 4:- is a curve expressing the relation of current and frequency in a resonant clrcult.

Referring to Fig. l, the direct-current motor 1, supplied with current from con-- ductors 2, 3, has a shunt field 4 in series with which is an adjustable resistance 5.

This resistance'should have a greater value than that required to vary the speed ofthe motor for ordinary operation. Around the resistance is a shunt circuit consisting of old of the" exciting ma conductor 6, vibrating contacts 7 and conductor 8. A switch lever opening and .clos-' ingthe contacts 7 is controlled by relay magnet 9, which has two opposing windings, one being permanently connected across the supply conductors 2, 3 by conductors 10, 11, and the other connected to supply conductors 2, 3, through conductors 10, 12, vibrating contacts 13 and conductor 11. The switch lever '14 controlling the contacts 13 is actuated by electromagnet 15. The magnet 15 isenergized by current from an alternating-current generator 16 mounted on a common shaft with the motor 1. The generator, although here shown as a -three-phase generator, may have any number of phases. The magnet in this case is shown as beingsupplied with current by means of conductors 17, 18 from ashunt transformer 19, the primary of which is connected across one of the phases of the alternating-current generator. In circuit with the magnet 15 is a condenser 20, which is so proportioned with reference to the inductance of the circuit that the circuitconare shown in condenser will be resonant to taining magnet 15, transformer 19, and the a frequency higher than the normal frequency of the generator 16. The motor and the alternator Fig. 1 as of the same order of size and directly connected, as in a motorgenerator set; but as already indicated above, the alternator'may be very small in comparison to the motor and, if desired, may be geared to the same to run at a higher spee a single-phase alternator 21 is belted to the motor, the rest of the system being understood to be similar to that shown in Fig.1.

The system shown in Fig. 3 is suitable for operation with a larger motor, the field of whichv is separately excited. Referring to this figure, the field 22 is energized. by exciter 23. The shunt field 24 of the exciter has a resistance 25 included in its circuit,

which is controlled by a relay magnet operating similarly to relay magnet 9 in Fig. 1. One winding of the relay magnet is directly connected across the exciter mains 26, 27 by means of conductors '28, 29, and the opposing winding is likewise connected across these mains by means of conductors 28, 30, contacts '31, and conductor 29. The contacts 31 are in this case controlled by an alternating-current magnet 15, which is similar to that :shown in connection with Fig. 1; but which operates in conjunction wlth a direct-current magnet 32 connected across the exciter mains, as clearly shown. In both Figs. 1 and 3sparkling at the contacts 7 1s su pressed by means of .condensers.

e operation of the -system illustrated ifi'Figul is as follows: As the speed of the motor l'tends to rise above normal, and the armature of the alternator 16 is, therefore, rotated at somewhat higher speed, the frequency of the alternating current tends to rise. The circuit of magnet 15 being resonant to a frequency This is illustrated in Fig. 2, in which.

mal frequency of the alternator 16, will tend to take more current because of the rise in frequency and voltage, as already explained. Contacts 13 will, therefore, close in turn causing the relay contacts 7 to close and shunting the resistance 5 in the field circuit of the motor. strength of the motor, and thus decrease its speed. The contacts 13, of course, will remain closed until the motor speed has returned to normal. As the resistance 5 is comparatively large, its corrective efiect will be almost instantaneous on the speed of the motor, and, therefore,'the contacts 13-will remain closed only 'a comparatively short time. The magnet 15 will ordinarily be operated at a frequency lower than that ofresonance, In Fig. 4: the range of frequencies at which the magnet 15 is efiective higher than the nor This will increase the field is indicated on the ascending ,branch of the curve between the ordinates 33, 34. If the speed of the. motor tends to fall below normal, and, therefore, the frequency of the alternator tends to fall below normal, the current taken by the magnet 15 will fall below that corresponding to the portion of the curve definedby lines 33, 34:, and the power of magnet 15 will not be suficient to close contacts 13; therefore, open, inserting the resistance 5 and weakening the motor field so as to increase its speed.

The operation of the system shown in Fig. 3 is similar to that described in connection with 'Fig. 1. An increase in the speed of motor way, as

1 above normal will in the same already described in connection with Fig. 1, increase the power of magnet 15, closing the contacts 31, which in turn causes relay contacts 7 to close and short circuits resistance 25 in the field circuit of the exciter. The exciter voltage will, therefore, rise, strengthening the motor field and decreasing its speed. The incr afse of exciter voltage will cause the magnet 32 to draw down its core, maintaining the contacts 31 closed for a little longer interval of time, until the speed of motor 1 has fallen '05 sufiiciently to decrease the frequency of the alternator, causing magnet 15 to open contacts 31 and lowering the volta e of theexciter. The effect of magnet 32 1s, therefore, to lengthen the intervals during which contacts 31 are opened or closed, enabling the motor 1 to change its speed back to normal. It is obvious, of course, that the alternating-current generator in this figure, as well as in Fig. 1,

by Letters Patent of the United States, is,- Y

' 1. The combination'of'aeource of power,

an alternating current generator driven thereby, and means for varying the speed of said source of power, said, means being responsive to changes of voltage and to changes of frequency of the current from said generator.

2. The combination of'a motor, an alter nating current generator driven thereby, a resistance in the field circuit of said motor and a make and break device for-periodically short circuiting said resistance, the

relative length of the intervals of make and break being responsive to variations of frequency of the generator current.

The combination of a motor having a shunt field winding, a resistance in the field circuit of the motor, an alternator driven by said motor, electromagnetic means operated by current derived from the alternator 'for shunting said resistance, said means being included in a circuit resonant to a frequency higher than the normal frequency of the current generated in the alternator.

In witness whereof, I have hereunto set my hand this 5th day of January 1909.

ALLEN A. TIRRILL.

Witnesses:

BENJAMIN B. HULL, HELEN ORFORD. 

